Magnetoresistive transducer including interdiffusion layer

ABSTRACT

A magnetoresistive transducer has a sensor which includes a magnetic layer and an interdiffusion layer. An active central region of the sensor extends between two passive end regions which are used to magnetically bias the active central region longitudinally. The biasing function is attained by fabricating the transducer on a wafer in an H-configuration, with the crossbar of the H as the active central region and a portion of the side legs as the passive end regions. When short current pulses are passed through the side legs of the H, the associated heating of the side legs (but not the crossbar of the H) causes interdiffusion between the interdiffusion layer and the magnetic layer and transforms the magnetic layer from soft magnetism to hard magnetism as required for the biasing function. The wafer is diced near the crossbar of the H and then processed further to form the finished transducer.

FIELD OF THE INVENTION

The present invention pertains to the field of magnetoresistive sensorsfor reading data in a magnetic recording device. More particularly, thepresent invention pertains to applying a selective pulse interdiffusionprocess for biasing the magnetoresistive sensors.

BACKGROUND OF THE INVENTION

In the field of magnetic recording devices, data such as computerprograms, databases, spreadsheets, etc. are usually stored onto amagnetic medium as a series of binary bits. Typically, the magneticmedium takes the form of a circular disk which is rotated about aspindle. A transducer, also known as a "head", is used to write bits ofdata onto the spinning circular disk. Sometimes the same head is alsoused to read the bits of data off the spinning disk. In other instances,a separate head is used in the reading process in order to realizegreater areal density for storage.

One such type of heads used only for reading data, is referred to asMagnetoresistive sensors (MR Sensors). MR sensors comprise a segment ofsoft-magnetic material whose electrical resistance varies when subjectedto a varying magnetic field. This effect is used in MagnetoresistiveRecording Heads (MR Heads) to sense the information recorded alongtracks of a magnetic recording medium.

FIG. 1 illustrates the principle of operation of an MR sensor whoseactive part comprises a rectangular piece of magnetoresistive material101 with a longitudinal axis, "a", parallel to the recording medium anda transverse axis, "b", which is perpendicular to the recording medium.A sense current, "I", flows along the longitudinal axis of the sensorhaving a resistance R₀. The electrical voltage across the sensor variesin a well known fashion with the orientation, θ, of its magnetization,M, as V=I. R₀ (1+c_(mr)) cos² θ, where c_(mr) is the magnetoresistivecoefficient of the sensor material and θ is the angle between thecurrent, I, and the magnetization, M. Magnetic fields, H_(s), from therecording medium produce variations of θ that are linear relative to,H_(s), when the quiescent orientation of the magnetization, θ₀ isroughly at a 45° angle relative to the current. This is achieved byinjecting suitable amounts of magnetic biasing flux into the sensingsegment, such as to provide for flux continuity along both axis.

This necessitates a biasing flux M_(t) =M sin θ₀ along the transverseaxis and a biasing flux M₁ =M cos θ₀ along the longitudinal axis. Hence,a complete sensor embodiment includes transverse and longitudinalbiasing means in addition to the sensing segment. The need fortransverse biasing provisions has been recognized early, and severalbiasing schemes have been disclosed in the prior art. They typicallyemploy a laminate of magnetic and nonmagnetic films such that thesensing current, I, generates a transverse magnetic biasing flux withinthe magnetic laminate circuit.

For instance, the well known Soft-Film Biasing scheme shown in FIG. 2(a)comprises an MR film segment (MR) 201 and a Soft-Film Biasing segment(SB) 202 in a plane-parallel position with each other. The two films areseparated by a Spacer segment (SP). The spacer may be quite thin (e.g.,200 A), as it only serves to break the magnetic "exchange coupling"between the MR 201 and the SB 202 film. The sense current, I, flowingthrough the less resistive (MR) segment 201 saturates the (SB) segment202 of the appropriate thickness in a perpendicular direction to produceS the required biasing flux, M_(t).

Mutual biasing schemes like the one shown in FIG. 2(b), employ twoidentical MR films (MR1) 203 and (MR2) 204 in a plane-parallel position.Here, the sense current is equally divided between the two films 203-204such that the films mutually bias each other, with the magnetization M₁and M₂ rotated in opposite directions. This embodiment is designed tooperate in a differential mode with the output signal proportional tothe difference in field seen by the two MR segments.

The main difference between the single MR element device of FIG. 2(a)and the dual element device of FIG. 2(b) is that the spatial resolutioncapability of the former relies on the presence of two magnetic shields(not shown) enclosing the sensor and is governed by the spacing betweenthe two shields. In contrast, the spatial resolution capability of thedifferential device is inherent and governed by the spacing between thetwo MR elements.

These and other transverse biasing schemes are well known and practicedin the prior art. The need for longitudinal biasing had also beenrecognized, but its practical realization proved to be more difficult.This is because in contrast to transverse biasing, one cannot readilyutilize the sense current to activate a longitudinal biasing circuit.Consequently, the disclosed longitudinal biasing schemes employ sometype of permanent magnet configuration in thin film form forlongitudinal biasing. These embodiments require elaborate fabricationsteps and are afflicted with a variety of problems and limitations.

For example, U.S. Pat. No. 4,639,806 issued to Kira and U.S. Pat. No.4,663,685 issued to Tsang, recognized the need for having longitudinalbiasing means attached to the MR sensing segment. Kira and Tsangconstructed such means in similar fashion, namely by superpositioning ahard-magnetic film onto the end regions of the MR sensor. Theseend-segments then become inactive because of the presence of thehard-magnetic film and because of the presence of an additionalconducting film over the same area. The two inventions differ in thatKira's hard magnetic film is ferromagnetic whereas Tsang's hard-magneticfilm is antiferromagnetic (producing no external magnetic flux). In bothcases, these longitudinal biasing means accomplish the "freeze" of themagnetization within these end-regions.

In an additional process step, a large external magnetic field is usedto magnetize the end-segments along the longitudinal direction andthereby create longitudinal biasing flux. In Tsang's invention, thebiasing flux equals the magnetization of the MR film. Kira's methodinjects an additional amount of flux that equals the magnetization ofhis ferromagnetic biasing film. Having too much biasing flux isundesirable as it renders the sensitivity within the sensor segmentnon-uniform, quenching it toward the attached end-segments. Someadjustment is possible, however, by magnetizing the end-segments at somecanted angle relative to the longitudinal direction.

The main problem with both inventions is that their longitudinal biasingmeans do not control the magnetization within the soft-magnetic biasingfilm. This causes unstable operation and pick-up of extraneous magneticsignals from the end-regions. These prior art embodiments are also quitenon-planar, which produces a loss of spatial resolution capability.

These flaws are corrected in U.S. Pat. No. 4,713,708 by controlling themagnetization of both the MR film and the SB film underneath theend-regions. This is achieved at the expense of added fabricationcomplexity. Additionally, there is the problem of accurate alignmentbetween the different layers and the preclusion of in-situ deposition.

U.S. Pat. No. 4,771,349 seeks to allow for in-situ deposition of allfilms comprising the sensing segment. This is achieved by subsequentlyremoving, under the end-regions, the SB and SP layers and thensuperpositioning the longitudinal biasing means over the underlying MRlayer only. The main problem with this approach is fabricationcomplexity and the creation of partial heterogeneous junctions withinthe current path.

The objective of U.S. Pat. No. 5,018,037 is to simplify fabricationrequirements by constructing contiguous sensing and biasing segmentswithout any layer in-common. A problem with this invention is thecreation of a heterogeneous junction in the current path.

U.S. Pat. No. 5,005,096 utilizes a hard-magnetic film to cause"magnetostatic biasing" of the MR sensing configuration. There is nophysical contact and hence no magnetic exchange coupling active betweenthe hard-magnetic film and any magnetic part of the MR sensor. Instead,the biasing flux is injected at the boundary between sensing and endregions as defined by a superpositioned conducting layer. Thedisadvantage of this invention is that magnetostatic control does notrender the end-segments totally inactive. Thereby, substantial pick-upof extraneous magnetic signals occurs from the end-regions.

U.S. Pat. No. 4,589,041 describes a differential sensor which uses apair of plane-parallel MR segments that mutually bias each other in thetransverse direction as is shown in FIG. 2b. Such a design is ofparticular interest as it offers substantially unlimited spatialresolution capability without the use of magnetic shields. However, theteachings of this invention do not include associated longitudinalbiasing provisions and no prior art biasing scheme is readily applicableto a differential sensor design.

Thus, there is a need in the prior art for improvements in thelongitudinal biasing provisions and there are no known biasing schemesthat satisfy the requirements of differential sensor embodiments. Theneeded improvements relate to the simplicity of fabrication, the sensorsspatial resolution capability and its long-term reliability. It is theobjective of this invention to provide these improvements.

SUMMARY OF THE INVENTION

In the "Selective Pulse Interdiffusion" (SPI) process, the areasdestined to become biasing segments of an MR Head are selectively heatedsuch that some specific layers of the sensor laminate interdiffuse toproduce a magnetic layer that has permanent magnet characteristics.Heating is done with one or more electrical current pulses whoseduration is short enough as to spatially confine heating to the biasingsegment. In one embodiment, a ladder-arrangement of sensors on the waferallows the SPI process to be performed collectively on a plurality ofsensors simultaneously.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated by way of example, and not by wayof limitation, in the figures of the accompanying drawings and in whichlike reference numerals refer to similar elements and in which:

FIG. 1 illustrates the principle of operation of a prior art MR sensorwhose active part comprises a rectangular piece of magnetoresistivematerial with a longitudinal axis parallel to the recording medium.

FIG. 2(a) shows a prior art Soft-Film Biasing scheme comprising an MRfilm segment and a Soft-Film Biasing segment in a plane-parallelposition with each other.

FIG. 2(b) shows a prior art mutual Biasing scheme employing twoidentical MR films in a plane-parallel position.

FIG. 2(c) shows a magnetization configuration for a dual element MRsensor.

FIG. 3(a) shows an MR sensor having a hard-magnetic layer as formed bythe selective pulse interdiffusion process.

FIG. 3(b) shows an MR sensor formed from an interdiffusion layersandwiched between two soft-magnetic layers.

FIG. 3(c) shows a differential MR sensor formed from the SPI process.

FIG. 4(a) shows a sensor geometry that electrically is a four-terminaldevice in an H-configuration of a wafer.

FIG. 4(b) shows an H-shaped sensor configuration with the conversioncurrent flowing through both legs for conversion into hard-magneticbiasing segments.

FIG. 4(c) shows the sensor configuration after fabrication of the MRhead has been completed.

FIG. 5(a) shows the SPI conversion process as applied to a singleelement.

FIG. 5(b) shows the SPI conversion process as applied to a column ofH-shaped elements.

FIG. 5(c) shows a method for interconnecting such H-configurations suchas to perform the conversion procedure simultaneously on a plurality ofMR sensors simultaneously on the wafer.

DETAILED DESCRIPTION

A selective pulse interdiffusion process for MR sensors is described. Inthe following description, for the purposes of explanation, numerousspecific details such as currents, durations, fabrication steps, biasingtechniques, etc., are set forth in order to provide a thoroughunderstanding of the present invention. It will be apparent, however, toone skilled in the art that the present invention may be practicedwithout these specific details. In other instances, well-knownstructures and devices are shown in schematic form in order to avoidunnecessarily obscuring the present invention.

The present invention is directed to an improved longitudinal biasingmethod that may be used with all the different sensor configurations. Inorder to understand these improvements, one needs to be aware of severalsensor fabrication and functional requirements described below.

The longitudinal biasing provisions should not adversely affect thesensitivity and uniformity of response characteristics of the sensorsegment, either by degrading its intrinsic response characteristics orby providing a mismatched amount of biasing flux. The optimal amount ofinjected flux equals the longitudinal flux component of the sensorsegment in combination with the transverse biasing provisions.

In order to have a sensor embodiment having a high spatial resolutioncapability, the sensor should be thin and planar. Also, the longitudinalbiasing provisions may not contain soft-magnetic elements which wouldotherwise channel extraneous magnetic flux-signals into the sensingsegment.

Given that the output signal is proportional to the sense currentamplitude, it is very desirable that there be no junction ofheterogeneous materials in the current path that would limit the currentamplitude due to electromigration and/or galvanic corrosion effects.Furthermore, since the individual layers comprising the active sensorsegment are very thin, their electrical and magnetic properties are muchaffected by surface characteristics. Good reproducibility of operatingcharacteristics can hence be obtained only if the sensor configurationis fabricated with all layers vacuum-deposited sequentially withoutintermitted exposure to a non-vacuum environment.

Moreover, the longitudinal biasing method should not be limited to aspecific sensor embodiment, but instead, should be applicable to avariety of different designs, including the ones using a pair of MRsensors in differential sensing schemes. In addition to the above, thereare the obvious requirements that the fabrication of the sensorembodiment be least complex such as to reduce manufacturing cost andprovide a high fabrication yield.

One key advantage of the SPI process is to produce hard-magnetic biasingsegments from the same laminate that comprises the sensing segment. Thisallows one to deposit the complete sensor assembly in-situ withoutintermitted exposure to non-vacuum conditions. Furthermore, this yieldsa configuration having no heterogeneous junction in the path of thesense current between the sensing and the biasing segments.

In the present invention, the different magnetic responsecharacteristics of the sensing and the biasing segments are thereforeestablished not by means of using different materials and fabricationprocesses, as has been done in the prior art, but instead by means of asubsequent conversion process on the regions destined to provide thebiasing function. This conversion is accomplished by heating the sensorlaminate within the biasing region for a certain time period above acritical conversion temperature. The heating causes an interdiffusion ofconstituents between certain layers of the sensor laminate.

Consequently, the present invention employs at least one pair of layersmade of different materials. These layers are deposited in intimatecontact with each other. FIG. 3(a) shows, on the left-hand side, a crosssection through an MR sensor 300 comprising: a soft-magnetic layer (S)301 and an interdiffusion layer (I) 302. When heated above theconversion temperature, the two layers interact such that the magneticcharacteristics of the S-layer 301 are transformed from soft-magnetic,having a coercive force of approximately less than 1 Oersted, tohard-magnetic (H), having a coercive force of say more than 100 Oersted.The transformed areas can thus provide the longitudinal biasing segmentsfor the MR sensor. A cross section through a transformed area is shownon the right side of FIG. 3(a). It contains the hard-magnetic layer (H)303 which performs the longitudinal biasing function.

The transformation from a soft-magnetic film (S) to a hard-magnetic film(H) results from an interdiffusion of some constituents to the twofilms, a process that is aided by the thinness of the layers. The changein magnetic properties of the soft magnetic layer can be quite dramaticfor certain choices of materials, even though the amount ofinterdiffused constituents may be small and does not change the materialcomposition appreciably.

For MR head applications, there are, of course, additional requirementsimposed upon the choice of materials, than solely the ability to undergosuch a magnetic conversion. The S-layer is typically an active componentof the MR sensor configuration (i.e., either the MR sensor itself or acomponent of the transverse biasing provision). The traditional choicefor this layer has been "Permalloy", either in its pure or doped form,depending whether or not a magnetoresistive response is required. Othersoft-magnetic materials may also be usable and are within the scope ofthis invention. The requirements for the I-layer characteristics placesa restriction that its presence does not adversely affect the responsecharacteristics of the S-layer in the sensing region, but after exposureabove the conversion temperature, it interacts with the S-layer toproduce a substantial increase of the coercivity in the latter.

Ideally, the I-layer is an inherently required component within thesensing region as with the laminate structure shown on the left in FIG.3(b). In other words, the I-layer 304 is interposed between the S2 layer305 and the S1 layer 306. By analogy, the I-film is the spacer (SP)between the (MR) film and the (SB) film of FIG. 2(a). After having beenheated above the conversion temperature, both the (MR) film and the (SB)film attain hard-magnetic characteristics. This is depicted on the rightof FIG. 3(b) as the two H-layers 307 and 308.

The laminate structure shown in FIG. 3(c) is representative of thedifferential MR sensor shown in FIG. 2(b). Here, the I-films 309 and 310serve as the adhesion-layers for the S1 and S2 films 311 and 312 (i.e.,MR1 and MR2 ). Both of these layers 312-313 attain hard-magneticcharacteristics after the conversion process. As these examples suggest,the longitudinal biasing scheme of the present invention can be usedwith any of the different disclosed MR sensor designs and without addingadditional layers to the fabrication of the sensing region.

Potential choices for the I-layer may be gained from the publishedresults of many investigations related to the choices of materials inthe construction of transverse biasing embodiments. Some investigationsinclude the choice of materials to be used as underlayer to the S-layerfor the sake of promoting adhesion to the substrate. Otherinvestigations include the choice of materials to be used as spacerlayers for breaking the exchange coupling between two soft-magneticfilms within the transversely biased sensing region. Investigators havealso studied the effects of raised temperatures on the materialcharacteristic in such laminates in order to ascertain that nodetrimental changes would occur due to temperature elevations associatedwith certain wafer processing steps. This work served to reject choicesof materials that did incur symptoms of temperature induced changes.

Guidance to the selection of suitable materials for this invention canbe gained from these works, except that the interest is rather opposite.Namely, the interest is in materials that do change theircharacteristics after exposure to elevated temperature (provided thatthe changes occur only at temperatures well above the highest waferprocessing temperature). Suitable choices for the I-layer can be foundwithin the family of refractory and certain transition metals. Severalsuch metals can satisfy the requirements in that they do not, withoutexposure above about 180° C., degrade the soft-magnetic characteristicsof the S-layer but do provide the hard magnetic characteristics to thislayer after having been exposed to temperatures approximately above 300°C. Examples of suitable choices of materials for the I-layer are:Titanium (Ti), Tantalum (Ta), Chromium (Cr) and possibly others from thefamily of refractory and transition metals. There may also be suitablematerial choices other than refractory and transition metals thatsatisfy the requirements of this invention.

After selecting the proper materials, there still remains the step ofaccomplishing heating within precisely defined boundaries (to anaccuracy of better than 1 um) in order to achieve the properinterdiffusion. The difficulty is that lateral spreading of heat maycause an ill-defined conversion boundary. This problem is solved in thepresent invention by heating the conversion areas over a time-periodthat is short enough such as not to allow excessive lateral spreading ofheat. Calculations and experiments have shown this is possible if theheating time is less than approximately one micro second. This makes itnecessary to reach the conversion temperature within an even shortertime period, approximately one-tenth of a micro-second.

Such rapid heating requires the application of power densities in theorder of Megawatts per square centimeter over the conversion area. Thiscan be accomplished by galvanic heating by using an electrical currentflowing through the conversion region. Because the cross section of thelaminate is quite small, conventional pulse generators can readilysupply the required pulse-currents with sufficient amplitude andshortness of duration. After a pulse has been applied, the area coolsrapidly with the heat flowing into the wafer substrate. A plurality ofsuch heating cycles may be used to complete the conversion process. Witha typical cooling time that is about ten times longer than the pulselength, the SPI process takes about ten times longer to complete (as ifthe material had been kept continuously at the conversion temperature ).

Once selected regions of the sensor configuration have been convertedfrom the soft-magnetic sensing structure into a hard-magnetic biasingstructure, there remains the step of defining a path for the SPIcurrent, such that the current flows only through the conversion segmentbut not through the sensing segment. The conventional MR sensor iselectrically a two-terminal device with the sensing current flowingthrough both the biasing and sensing regions. Any such flow-patternwould not be usable for the SPI process, as it would affect the sensingand biasing regions similarly.

To perform the SPI process, one needs to pattern the deposited laminateat each sensor location into an H-configuration as is shown in FIGS.4(a)-(c). This geometry represents electrically a four terminalconfiguration as is shown in FIG. 4(a) having terminal points 408 and409 at the ends of leg 402 and terminal points 410 and 411 on the endsof leg 403. The cross-bar 401 of the "H" is to remain the soft-magneticsensing laminate while the two vertical bars 402 and 403 of the "H" areto be converted into the hard-magnetic biasing laminate. The conversionis performed as is depicted in FIG. 4(b) by sending the SPI current,I_(c), flowing through the legs of the "H", thereby converting theseregions into a hard-magnetic laminate. The legs may be converted one ata time by first sending the SPI current from terminal 408 to terminal409 and subsequently from terminal 410 to terminal 411. Alternatively,both legs may be converted at the same time simultaneously sending theSPI current from the terminals 408 and 410 to the terminals 409 and 411.In either case, none of the SPI current flows through the cross-bar 401.In the first case, because there is no electrical connection through theother leg and in the second case, because of symmetry, there is nodifference in electrical potential across the cross-bar.

FIG. 4(c) shows the sensor configuration after the fabrication of the MRhead has been completed. It can be seen that the lower portion of theH-configuration has been removed by lapping as performed in the courseof the conventional sequence of head fabrication steps with the face 406now being planar with the head's air bearing surface. Note that theconfiguration has become the standard 2-terminal MR sensing device withthe sense current, I, applied as indicated.

Furthermore, several such H configurations can be electricallyinterconnected, as is shown in FIGS. 5(a)-(c), to allow simultaneousconversion on a plurality of H-configurations on the wafer. Theinterconnections may be made of the sensor laminate itself, or,preferably of a superpositioned lead metallurgy as is also being usedfor connecting the MR sensor to its external terminal connections.Again, the SPI interconnections between sensor elements are subsequentlyremoved when the wafer is being diced and lapped into individual slidersduring the conventional sequence of head fabrication steps. Theremaining parts on the slider are the required external terminalconnection.

The conversion procedure is depicted as illustrated in FIG. 5(a) for asingle element with the voltage difference V+/V- applied one or both ofthe legs 501 and 502 as discussed above. FIG. 5(b) shows a column ofH-elements interconnected into the form of a ladder whose rungs 503-506are to become the sensing regions and the rails 507-514 are destined tobecome biasing regions of the MR configuration. Note that the wholeladder of H-elements form the required four-terminal device. In contrastto the single element process, the SPI conversion procedure on aconversion ladder needs to be carried out with the SPI current flowingsimultaneously through both legs in order that there be no voltagedifference across the rungs of the ladder. A conversion ladder mayinclude all H-elements within a column on the wafer or it may includeonly a portion of a column. Also, a plurality of such ladders may beconnected in parallel as is shown in FIG. 5(c). Given enough availablepulse current, the conversion procedure may be carried outsimultaneously on all H-elements 515-526 on the wafer.

The SPI invention can be used with a variety of MR sensorconfigurations. Schemes using different transverse biasing methods, forinstance, differ in the detailed structure of the laminate comprisingthe sensor region. As long as this laminate is assembled with aninterdiffusion film in contact with each soft-magnetic film, the SPImethod can convert any chosen region of the laminate into ahard-magnetic biasing region. In short, the present invention provides alongitudinal biasing method that is broadly applicable to sensorembodiments using different transverse biasing schemes in single-endedor differential sensing implementations.

A fabrication process is now described for a differential type MRsensor. In this embodiment, fabrication starts with sequentiallyvacuum-depositing the laminate of continuous thin metallic films onto asuitable substrate. The substrate typically is a ceramic materialsuitable to lastly be cut and shaped by well known fabrication stepsinto a plurality of sliders. The laminate for this differentialconfiguration comprises the five films: I1, S1, SP, S2, I2 (as shown inFIG. 3(c)), with an optional protective passivation film, such asAlumina (not shown) on top of I2. The structure may be altered to thesequence S1, I1, SP, I2, S2 or I1, S1, SP, I2, S2 without substantiallychanging sensor function or the conversion process.

The Interdiffusion Films, I1 and I2 are on average 150 A thick (i.e., 30to 300 A) and made of Titanium (Ti) or a similar refractory metal. TheSensor Films, S1 and S2, are on average 400 A (i.e., 200 to 800 A) thickand are made of Permalloy or another soft-magnetic material thatexhibits a suitably large magnetoresistive effect. The Spacer Layer, SP,has a thickness of approximately 3000 A (i.e., 1000 to 8000 A), such asto space the Sensor films, S1 and S2 by a distance less than the desiredspatial resolution capability. Its electrical conductance should be lowso as not to shunt the sensor current but it need not insulate S1 fromS2 since they will be connected in-parallel. In principle, the spacerlayer and the interdiffusion layer could be one and the same (as shownin FIG. 3(b)). However, suitable interdiffusion materials tend toproduce too much of a shunting conductance. Hence, it is advantageous toemploy an insulating material, such as Alumina as a spacer layer (assuggested by FIG. 3(c)).

The subsequent processing steps serve to pattern the laminate intoH-shapes and to fabricate a lead-metallurgy to establish the requiredelectrical connections. All these steps are done by means of well knownphotolithographic process steps using subtractive methods, such asion-milling or additive "lift-off" methods. The geometry of the leadmetallurgy has to be such as to enable the simultaneous SPI conversionon a plurality of elements and to provide for the sensor's externalterminal connections on the slider. The requirements for both functionsare identical: to provide for a low resistance electrical connection tothe sensor such as to have a minimum of extraneous power dissipation.

If the sensor laminate is passivated with an insulating layer (e.g.,Alumina), one needs to etch via-holes through the passivation whereverone wants to establish an electrical connection between the lead and thelaminate metallurgy. Such via-holes can be etched chemically with themetallic laminate serving as an etch-stop. Next the lead metallurgy,made of copper, aluminum, or gold or a similarly well conductingmetallic alloy is deposited as a continuous layer onto the passivationlayer. It is subsequently patterned into the desired lead configurationusing ion-milling for instance. Note that all of the above process stepsare essentially identical to the steps required to fabricate the sensorconfiguration without longitudinal biasing provisions.

Now the assembly is ready for the SPI conversion process. This is doneby connecting an electrical pulse generator to the SPI contact pads andsending current pulses through each conversion region. In the currentlypreferred embodiment, a pulse amplitude of 1 ampere is required to heat10 um wide conversion segments above the threshold temperature. A pulselength of 0.1 usec at a duty-cycle of about 10% is used to accomplishthe SPI conversion with a sufficiently sharp definition of theconversion boundaries. The total time required for the SPI conversionprocedure depends on the pulse length, amplitude and duty-cycle. It canrange from 0.1 to 1000 seconds, but is typically about 10 seconds. Inother embodiments, the conversion segments can range in width from 5 to50 um. The pulse length can be varied from 0.1 to 1.0 usec with avariance in the duty cycle of 1% to 20%.

Finally, the wafer is diced into individual rectangular shapes, eachcarrying at least one sensor configuration near the edge which is tobecome the air-bearing surface (ABS) of the recording head. The ABS edgeis lapped in a conventional fashion partly into the sensor stripe toyield the final configuration (as shown in FIG. 4(c)). The lappingprocess removes the lower parts of the H-shapes and connecting leadmetallurgy and also effects the final height of the sensor stripe. Theupper part of the H-shape and lead metallurgy remains on the slider andcomprises the sensor configuration with lead metallurgy of the finishedMR recording head.

The last step in the fabrication of an MR sensor configuration is tomagnetize the hard-magnetic end regions along a substantiallylongitudinal direction. This is done by applying an external magneticfield of sufficient magnitude to saturate the biasing region along thespecified direction. The end regions may be magnetized at a somewhatskewed angle relative to the longitudinal axis such as to inject anoptimal amount of biasing flux into the active region. Thisinitialization procedure can be carried out in unison on all sensors onthe wafer. Traditionally it is often performed individually incombination with a head testing procedure on the finished headembodiment. If the embodiment is of the shielded type, then themagnitude of the initialization field must exceed the coercive force ofthe hard-magnetic region in addition to the file required to saturatethe magnetic shields.

This initialization procedure renders all longitudinal biasing regionsuniformly magnetized along the same direction. Such biasing provisionsare in concert with the active sensing area having a magnetizationconfiguration as is shown in FIG. 2a for the single-element and in FIG.2(b) for the dual element embodiment.

However, in the case of the dual element sensor, the SPI method permitsone to employ a magnetization configuration as is shown in FIG. 2(c)that differs from the prior art configuration shown in FIG. 2(b). In theSPI configuration of FIG. 2(c), the orientation of the magnetization inthe two sensor elements is antiparallel with respect to each other. Thisorientation offers substantial performance advantages over the FIG. 2(b)orientation. In the antiparallel orientation both films have identicalspatial sensitivity characteristics which is not the case for the FIG.2(b) orientation where the sensitivity of one film is skewed to theright side of the sensor. However, an antiparallel orientation of themagnetization can be internalized and maintained by having a similarantiparallel orientation of the magnetization in the longitudinalbiasing segments which injects flux components of opposite polarity intothe two MR films of the active segment. The ability to initialize suchan antiparallel biasing configuration is a unique feature of the SPImethod. It happens because the SPI current flowing through the legs ofthe H-configurations produces longitudinal magnetic fields that areantiparallel in the superpositioned biasing segments. The resultingantiparallel magnetization in the end-regions force the magnetization inthe active region into a similarly antiparallel state. Theinitialization of the antiparallel magnetization configuration as isshown in FIG. 2(c) is hence an automatic feature of the SPI method thatoccurs without the application of the traditional externalinitialization field.

The existence of an antiparallel magnetization configuration in theactive and passive sensor areas offers other advantages. Since there isno net-magnetic flux passing through any cross section through thesensor, this configuration inherently offers improved stability of theinitialized configuration against external magnetic disturbances.

In an alternative embodiment of the present invention, a conventionalsingle-element MR-sensors relies on the use of magnetic shields forattaining its spatial resolution capability. A suitable laminateemploying the Soft-Film Biasing method is depicted in FIG. 3(b) with S1being the soft-bias film and S2 being the MR film The interdiffusionfilm, I, also serves the function of the traditional spacer layer, SP,used to break the magnetic exchange coupling between S1 and S2. Thefabrication of this other embodiment differs in that it requires one tofirst fabricate a magnetic shield (typically about 1 um thick Permalloy)and a superpositioned spacer/insulation layer on the substrate.Similarly, the fabrication process is concluded with the additionalsteps of depositing a second spacer/insulation layer and a secondmagnetic shield on top of the sensor configuration. The magnitude of theinitialization field must be large enough such as to saturate theshields and then exceed the coercive force of the hard-magnetic biasingregions.

Note that in the present invention, the sensing and biasing provisionsof the entire MR sensor configuration are fabricated from the samelaminate. The laminate may be deposited in-situ without intermittedexposure to non-vacuum conditions. Furthermore, the SPI processoptimizes the reliability of operating the MR sensor because theconfiguration has no heterogeneous material-junctions along the currentpath. In addition, the present invention provides a sensor configurationthat can provide optimal spatial resolution capability since thelongitudinal biasing segment is perfectly planar with the sensingsegment and does not contain any soft-magnetic elements.

Thus, a selective pulse interdiffusion process for magnetoresistivesensors is disclosed.

What is claimed is:
 1. A magnetoresistive read transducer comprising:asensor configuration having passive end regions separated by an activecentral region; a first layer of a magnetoresistive conductive material,said magnetoresistive conductive material containing a nickel-ironalloy; a second layer of nonmagnetic material in contact with said firstlayer and extending over said active central region and said passive endregions, said nonmagnetic material containing a member of the groupconsisting of titanium, tantalum, chromium, and the refractory andtransition metals, wherein the passive end regions have been heatedabove an activation temperature, thereby causing an interdiffusionbetween the materials of the first and second layers, and wherein saidinterdiffusion has transformed the magnetic characteristics of the firstlayer from soft-magnetic to hard-magnetic such that said passive endregions provide longitudinal magnetic biasing of said active centralregion.
 2. The magnetoresistive transducer of claim 1, wherein saidpassive end regions have been heated to above the activation temperatureby passing an electric current through said end regions.
 3. Themagnetoresistive transducer of claim 2, wherein the passive end regionscomprise a magnetic alloy having permanent magnetic properties.
 4. Themagnetoresistive transducer of claim 3, wherein the first layer of theactive region comprises a soft magnetic layer and the second layer ofthe active region comprises an interdiffusion layer.
 5. Themagnetoresistive transducer of claim 4, wherein the interdiffusion layeris comprised of titanium.
 6. The magnetoresistive transducer of claim 4,wherein the interdiffusion layer is comprised of tantalum.
 7. Themagnetoresistive transducer of claim 4, wherein the interdiffusion layeris comprised of chromium.
 8. The magnetoresistive transducer of claim 4,wherein the electric current is a current pulse whose amplitude heatsthe passive region above the activation temperature and whose durationis such that the heating does not spread substantially into the activeregion.
 9. The magnetoresistive transducer of claim 8, wherein aplurality of current pulses are applied sequentially and wherein a timeduration between current pulses allows the passive region to coolsubstantially below the activation temperature.
 10. The magnetoresistivetransducer of claim 2 comprising a first element having said first layerand said second layer and a second element having said first layer andsaid second layer wherein said second element is superpositioned uponsuch first element, each element having a active central region andpassive end regions wherein the magnetization in the two elements isantiparallel.
 11. A structure useful in fabricating a magnetoresistiveread transducer, said structure being formed in the shape of an H andhaving a crossbar and side legs, said structure comprising:a first layerof a magnetoresistive conductive material, said magnetoresistiveconductive material containing a nickel-iron alloy; a second layer ofnonmagnetic material in contact with said first layer, said nonmagneticmaterial containing a member of the group consisting of titanium,tantalum, chromium, and the refractory and transition metals, whereinthe side legs of the H have been heated above an activation temperatureby passing an electric current therethrough, causing an interdiffusionbetween the materials of the first and second layer in the side legs,and wherein said interdiffusion has transformed the magneticcharacteristics of the first layer in the side legs from soft-magneticto hard-magnetic.
 12. A plurality of the structures of claim 11, saidH-shaped structures being connected in a column so as to form a ladderarrangement.